1. Field of the Invention
The present invention relates to drum type washing machines, and more particularly, to an outer rotor type BLDC motor applicable to a direct coupling type drum type washing machine, and a method for fabricating the same.
2. Discussion of the Related Art
In general, a drum type washing machine washes laundry by using a friction force between a drum rotated by a driving power of a motor and laundry in a state detergent, washing water, and the laundry are introduced into the drum, shows almost no damage to, and entangling of the laundry, and has pounding, and rubbing washing effects.
In the related art drum type washing machines, there are an indirect coupling type in which the driving power is transmitted from the motor to the drum through a belt wound on a motor pulley and a drum pulley indirectly, and a direct coupling type in which a rotor of a BLDC motor is coupled to the drum directly, to transmit the driving power from the motor to the drum, directly.
The type in which the driving power of the motor is transmitted to the drum, not directly, but indirectly through the motor pulley and the drum pulley, has much energy loss in the course of power transmission, and causes much noise in the course of power transmission.
According to this, for solving the problems of the indirect coupling type drum type washing machines, it is the present trend that use of the direct coupling type drum type washing machines with the BLDC motor is increasing, as example of which there are Korean Laid Open Patent Nos. 2001-37517, and 2001-37518.
A related art direct coupling type drum type drum type washing machine and a structure of a motor thereof will be described with reference to FIGS. 1 to 6, briefly. FIG. 1 illustrates a longitudinal section of a related art drum type washing machine.
Referring to FIG. 1, the related art drum type washing machine is provided with a tub 2 mounted on an inside of a cabinet 1, and a drum 3 rotatably mounted on a central portion of an inside of the tub 2. There is a motor in rear of the tub 2, wherein a stator 6 is secured to a rear wall of the tub, and a rotor 5 surrounds the stator 6, and is connected to the drum 3 with a shaft passed through the tub.
In the meantime, there are a door 21 mounted on a front of the cabinet 1, and a gasket 22 between the door 21 and the tub 2.
There are hanging springs 23 between an inside surface of an upper portion of the cabinet 1, and an upper portion of an outside circumferential surface of the tub 2, and a friction damper 24 between the inside surface of a lower portion of the cabinet 1, and a lower portion of the outside circumferential surface of the tub 2.
FIG. 2 illustrates a perspective exterior view of the stator in FIG. 1, and FIG. 3 illustrates a perspective view of a divisional type core DC applied to the stator in FIG. 2.
In a related art method for fabricating the core, a sheet of metal plate is pressed to form a unit core having Ts 151, a base portion 150, and projected portions 500 opposite to the Ts 151 each for forming fastening hole 500a therein, the unit cores are stacked to form a unit core assembly, and the unit core assemblies are connected to each other in a circumferential direction, to complete fabrication of the stator core, called the divisional core DC.
The projected portion 500 provides the fastening hole 620a for fastening the stator 6 to the rear wall of the tub, and serves to endure a fastening force of a bolt.
However, the method for fabricating the stator 6 by means of the divisional cores DC has, not only a complicate fabrication process, but also loss of much material.
Therefore, even if a helical type core HC is favorable, in which a sheet of steel plate having the Ts 151 and the base portions 150 is stacked turning in a helix for reducing the material loss, and making the fabrication process simple, since it is required to bend the sheet of metal punched out in a shape of a stripe into the helix, the helical core has a drawback in that the projected portion for fastening the stator to the tub can not be formed on an inner side of the core.
This is because, if the projected portion 500 is formed on the inner side of the core in fabrication of the helical core HC, a large width of the core at a portion having the projected portion formed thereon impedes bending of the core.
Therefore, currently, for employing the helical type core HC, a stator structure is required, in which a function the same with the projected portion of the divisional core DC is made to be carried out, not by the core itself, but by other portion.
For reference, a reason why it is important to secure an adequate rigidity of the projected portion having the fastening hole formed in for fastening the stator to the tub is as follows.
The washing machine in which the drum is directly rotated by the BLDC motor has the stator mounted on a rear portion of the tub, directly. In a case of the motor for a large capacity drum type washing machine with more than 1.5 kg of stator net weight, and a spinning speed in a range of 600˜2000 RPM, it is liable that a fastened portion of the stator 6 is broken due to the stator weight, and vibration, shaking, and deformation of the rotor 5 in the high speed rotation.
Particularly, in a case of the drum type washing machine, in which the BLDC motor is used, and the stator 6 is secured to the tub rear wall, where an axis direction of the stator 6 is substantially parallel to ground, the vibration generated during operation of the washing machine causes intensive damage to the fastening portion of the stator 6 to the tub rear wall.
Thus, an adequate rigidity of the projected portion having the fastening hole formed therein is very important in fastening the stator 6 to the tub.
A related art outer rotor will be described with reference to FIGS. 5 and 6.
Referring to FIGS. 5 and 6, because the outer rotor R pressed of a steel plate (hereafter called as “steel plate rotor”) has a stepped portion along a circumferential direction formed on a sidewall 120 extended from a circumference of a bottom 110 of the rotor frame 100 perpendicular to a bottom 100 surface, to support magnets M when the magnets M are attached to an inside surface of the sidewall 120 of the rotor frame 100, fabrication of the outer rotor is easy.
Moreover, there are a plurality of radial cooling fins 130 around a center portion of the bottom 110 of the rotor frame 100 of the steel plate rotor R to blow air toward the stator (not shown) to cool down heat generated at the stator.
The cooling fins 130 are lanced toward an opened side of the rotor, and openings formed by the lancing serve as vent holes.
There are embossed portions 150 between adjacent cooling fins 130 on the bottom 110 of the rotor frame 100 for reinforcing strength of the rotor, and there are drain holes 160 in the embossed portions 150 for draining water.
However, the related art steel plate rotor R has the following problems.
Despite of anti-rusting heat treatment of a surface of the related art steel plate rotor R, rust occurs on a portion of the surface scratched during transportation or other situations.
The surface of the rotor also corrodes due to chemical reaction of detergent stuck to the surface of the rotor as the drum type washing machine is used for a long time.
In the meantime, during the spinning for water extraction, the sidewall 120 of the related art steel plate rotor 100 throbs intensely due to electro-magnetic interaction (attraction and repulsion) with the stator, leading to increase noise.